1. Field of the Invention
The present invention relates to novel multiple function dispersant viscosity index improvers comprising a polymer backbone grafted with at least a first functional group associated with sludge and varnish control and at least a second functional group associated with soot handling performance and viscosity control. The present invention also relates to methods for manufacturing the novel multiple function dispersant viscosity index improvers and lubricating oil compositions containing the novel multiple function dispersant viscosity index improvers.
2. Description of the Related Art
Conventional lubricating oils contain a variety of additives, each of which is used to control specific performance characteristics of the lubricating oil.
One common group of lubricating oil additives are dispersant viscosity index improvers having functional groups associated with sludge and varnish control. Among those additives known in the art to be useful as dispersant viscosity index improvers having functional groups associated with sludge and varnish control are polyolefins grafted with nitrogen-containing and/or oxygen-containing monomers. For example, U.S. Pat. No. 5,523,008 describes a dispersant viscosity index improver comprising N-vinylimidazole grafted onto a polyolefin backbone. U.S. Pat. No. 5,663,126 describes a polyolefin having one or more of N-vinylimidazole, 4-vinylpyridine, or other ethylenically-unsaturated nitrogen-containing and/or oxygen-containing monomers grafted to the polyolefin backbone.
Polyolefins grafted with nitrogen-containing and/or oxygen-containing monomers have been prepared by dissolving the selected polyolefin in a solvent, which is typically a lubricating oil base stock, and then mixing the polyolefin solution with a graftable monomer and an organic peroxide as an initiator at conditions effective to graft the graftable monomer to the polyolefin backbone. As described in U.S. Pat. No. 5,523,008, for example, the initiator can be added before, with or after the graftable monomer, but is desirably added so that the amount of unreacted initiator which is present at any given time is preferably a small fraction of the entire charge. The initiator may be introduced into the reactor in several discrete charges, or at a steady rate over an extended period. The organic peroxide initiators used in these processes create an inherently dangerous manufacturing environment.
The lubricating oil base stocks typically used as solvents for the grafting reaction are those having a low content of aromatics. As described in U.S. Pat. No. 5,663,126, for example, the base oil should disperse or dissolve the components of the reaction mixture without materially participating in the reaction or causing side reactions to an unacceptable degree. Thus, aromatic constituents are desirably kept to low levels (if present at all), since aromatic materials may be reactive with each other or other reaction components in the presence of initiators. The reaction components may thus either be wasted or produce unwanted by-products, unless the presence of aromatic constituents is small. For this reason Group II base stocks, which are essentially free of unsaturated aromatics, but which are expensive in comparison to Group I base stocks, are typically used as the solvent for the grafting reaction.
Another common group of lubricating oil additives are dispersant viscosity index improvers having functional groups associated with soot handling performance and viscosity control. Among those additives known in the art to be useful as dispersant viscosity index improvers having functional groups associated with soot handling performance and viscosity control are polyolefins grafted with the reaction product of an acylating agent and an amine. U.S. Pat. No. 4,320,019 describes dispersant viscosity index improvers prepared by first grafting a polyolefin with an acylating agent to form an acylating reaction intermediate and then further reacting the acylating reaction intermediate with an amine. U.S. Pat. No. 7,371,713 describes dispersant viscosity index improvers having functional groups associated with soot handling performance and viscosity control being prepared by first reacting an acylating agent, such as maleic anhydride, with an amine, such as an aromatic amine, and then grafting the product of that reaction onto a polyolefin.
Each additive is a separate component of the formulated lubricating oil and thus increases the cost of the formulated lubricating oil. Thus, it is beneficial to have a multi-functional additive that controls more than one performance characteristic of the lubricating oil. To that end, U.S. Patent Application Publication No. 2008/0293600 describes a multifunctional grafted polymer containing two functional groups grafted to a polymer backbone. A first functional group is associated with sludge and varnish handling and comprises ethylenically unsaturated, aliphatic or aromatic monomers having 2 to about 50 carbon atoms and containing oxygen and/or nitrogen. A second functional group is associated with soot handling performance and viscosity control and comprises the reaction product of an acylating agent and an amine.
As described in U.S. Patent Application Publication No. 2008/0293600, the process for preparing the multifunctional graft polymer is important. To achieve good performance with respect to both soot handling and sludge and varnish control, it is important to first graft an acylating agent, such as maleic anhydride, onto the polymer backbone, forming a polymer containing acyl groups, for example, succinic anhydride groups. Next, the monomer or monomer grouping associated with sludge and varnish handling, for example N-vinylimidazole, is grafted onto the polymer backbone. Finally, the amine or amines capable of undergoing a reaction with the acyl group is introduced and reacted with the acylated polymer thereby imparting soot handling performance to the graft polymer.
The multiple function dispersant viscosity index improvers of embodiments of the present invention provide numerous benefits over the multi-functional additives described in U.S. Patent Application Publication No. 2008/0293600. To prepare the multi-functional additive described in U.S. Patent Application Publication No. 2008/0293600, two different substituents are grafted to the polymer backbone. First, an acylating agent, such as maleic anhydride, is grafted to the polymer backbone. This grafting reaction typically involves the use of an initiator, such as an organic peroxide, and is typically performed in a Group II lubricating base oil. Second, the functional group associated with sludge and varnish handling, for example, N-vinylimidazole, is grafted directly to the polymer backbone. This grafting reaction also typically involves the use of an initiator, such as an organic peroxide, and is typically performed in a Group II lubricating base oil.
On the other hand, using embodiments of the present invention, only one substituent may be grafted to the polymer backbone. It has been found that the functional group associated with sludge and varnish handling may be the reaction product of an acylating agent and an amine. Accordingly, multiple function dispersant viscosity index improvers may be prepared using only one grafting reaction—the grafting of an acylating agent, such as maleic anhydride, to the polymer backbone. The grafted acylating agent may then be reacted with two different amines in order to produce the first and second functional groups. Thus, it has been found that multiple function dispersant viscosity index improvers may be prepared while minimizing the use of organic peroxide initiators and Group II lubricating base oils. As a result, it has been found that multiple function dispersant viscosity index improvers may be prepared at lower cost and in a safer and more environmentally friendly manufacturing environment.